Wave attenuation in periodic structures

A periodic structure acts as a filter for traveling waves of any kind whether they be electromagnetic, acoustic, bending or anything else. This principle has been used to reduce the vibration level in one part of a structure when it is excited at another. For example, certain frequencies from engine excitation can be attenuated in the cabin of an aircraft. In this paper we report analytical methods for predicting the attenuation of bending waves in a dissipationless beam with flexible ribs attached to it. The insertion loss (attenuation) spectra for a wide frequency range are then compared with measured results for test structures with 1 to 15 ribs attached. Some preliminary work was also done on the effect of rib spacing. The width of the attenuation band increased with increasing number of ribs with seven ribs giving almost as wide a band as it had for the infinitely long periodic beam. Since the structure has no dissipation, the attenuation is due solely to interference effects of multiple reflections.